Events and Actions 

Most UI elements (e.g. the Button UI element) can react to a user’s interaction (e.g. clicking on the corresponding pushbutton). This reaction can trigger a handling method to be called within the view controller.

Events are used to communicate between controllers and enable one controller to trigger event handlers in a different controller. Cross-component communication can be implemented using the interface controller’s events. Events that were created in the component controller are visible within the component only.

Action

Actions are runtime objects that associate a client-side event with a server-side response. When you create an action object, the system automatically creates an action handler method. You link the event, the UI element is equipped with, with the appropriate action object.

If a UI element has been inserted several times into a view, you can equip their events with different actions as necessary. The event is then processed by the corresponding event handler depending on the action that is linked.

Actions can also be reused within a view. This means that an action can be linked to the events of several (or even different) UI elements. In this manner, it is possible to write a single, generic action event handler method that can respond to a variety of events raised by multiple UI elements.

A view controller should be written such that it is only ever a consumer of data, never a generator. This means that view controllers should never contain coding to interact with a back end system.

Recommended Action Architecture

SAP strongly recommends the following architecture:

●      Once control has been passed to the action event handler method in the view controller, this method should delegate all interaction with the back-end system to a non-visual controller.

●      Hence the call to a method happens to live in the component controller. This method then interacts with the back-end system via the model object.

●      The data returned from the model object is passed from the component controller to the view controller through the technique of context mapping.

Inbound Plug Events

Inbound plugs in a view also react like an event. Therefore, when a view is called using an inbound plug, the event handler that is optionally available for the inbound plug is always called first. In this case event handling takes place within the current view controller, however.

The same applies for the inbound plugs of an interface view. In the corresponding window controller, an event handler is created. It can then be programmed further, as appropriate.